DSP-FLL for FSK demodulation

In this paper, we propose a DSP type Frequency Locked Loop (DSP-FLL) using a Frequency Difference Detector (FDD). Since the FDD is employed, the DSP-FLL is controlled by the frequency. Therefore, the transfer function becomes first order and ringing does not occur. Furthermore, it can be understood from the detection property of the FDD that the cycle slip does not occur and DSP-FLL can pull in the frequency up to half of the sampling frequency.